GATE 2014 CS (CS2) – Question 35
In the diagram, L1 is Ethernet and L2 is Token-Ring. An IP packet travels from S to R. Links within and across the two ISPs are point-to-point optical links. Initial TTL is 32. Find maximum TTL when R receives the datagram.
Practise this question in The GATE Grind →
Show answer and explanation
Correct answer: 26 to 26
Explanation
TTL decreases as the datagram is forwarded, so its largest received value corresponds to the shortest forwarding path. The official key uses six network hops, giving **32−6=26**. The diagram does not label forwarding-device types clearly; ordinary layer2 Ethernet/token-ring forwarding alone does not decrement IP TTL. The official value is retained without treating every LAN station as an IP router.